1. Field of the Invention
The present invention relates to disk drives for computer systems. More particularly, the present invention relates to a disk drive with improved shrouding.
2. Description of the Prior Art
A computer system usually includes one or more disk drives for economical, non-volatile data storage. FIG. 1 shows a typical prior art disk drive 100 which includes a housing formed by fitting a cover comprising an inner layer 102 and an outer layer 104 to a base 106 to create a sealed head disk assembly (HDA) chamber. The HDA includes one or more disks 108 stacked in a spaced-apart relationship on a spindle motor hub and rotated by a spindle motor (not shown). The disks 108 rotate in close proximity to a head 114 that is disposed by means of a head gimbal assembly (HGA) attached to one of a plurality of actuator arms 110.
The spindle motor includes a stationary element such as a fixed spindle shaft 116 affixed to the disk drive housing at the base and cover to define and stabilize a spindle axis about which a hub rotates the disks 108. A stator of the spindle motor, as well as bearings and seals, are secured between the fixed spindle shaft 116 and the rotating hub. The actuator arms 110 are part of a head stack assembly (HSA) that turns about a pivot bearing assembly by a voice coil motor (VCM) 112. The pivot bearing assembly includes a stationary element such as a pivot shaft that is fixed to the disk drive housing at the base and cover to define and stabilize a pivot axis for the HSA. Typically, the pivot shaft is rigidly coupled at the top to the cover and at the bottom to the base. The rigid attachment of the fixed spindle shaft and the pivot shaft fixes and stabilizes the relationship of the spindle axis and the pivot axis to control head positioning error. The actuator arms 110 move in response to energizing currents sent to the voice coil motor (VCM) 112 which moves the HSA on the pivot axis, swinging the actuator 110 arms to move the associated heads 114 over the associated disk surfaces.
It is desirable to transfer data to and from disks 108 rapidly. The data transfer rate increases with spindle motor rotational speed. However, there are a number of problems associated with higher spindle motor rotational speeds. One problem is increased internal air turbulence in the HDA which can excite disk flutter modes, thereby setting up resonances that can cause the heads 114 to move off track during read and write operations. Proper centerline tracking is imperative for faithfully writing data to, and reading data from the disks 108. Another problem associated with higher spindle motor rotational speeds is increased windage drag on the disks, thereby causing an increase in spindle motor current and elevated internal HDA temperature. Yet another problem associated with higher spindle motor rotational speeds is an increase in the acoustic noise radiated by the disk drive.
Shrouding the disks 108 can reduce internal air turbulence thereby attenuating disk flutter, windage drag, and acoustic noise. The prior art disk drive of FIG. 1 provides radial shrouding by molding the base 106 into a cylindrical form such that the disk 108 fits snugly within, leaving a very narrow gap between the spinning outer perimeter of the disks 108 and the inner surface of base 106. However, the radial shroud of the base 106 cannot extend into the gap 118 coextensive with the actuator arms 110 so that the HSA can be inserted into the base 106 during manufacture. When inserting the HSA, the actuator arms 110 are rotated such that they fit into the gap 118 without damaging the heads 114. The actuator arms 110 are then rotated to position the heads 114 over the disks 108. The air turbulence which forms in this gap 118 exacerbates the disk flutter, windage drag, and acoustic noise.
U.S. Pat. No. 5,898,545 to Schirle discloses a separate shroud piece which is inserted into the gap 118 and connected to the base 106 after installing the HSA. The separate shroud piece comprises air flow vanes and cams to facilitate “ramp loading” the heads 114 during spin down. Although the separate shroud piece improves the shrouding over the prior art disk drive 100 of FIG. 1, it must be precisely machined and then precisely mounted into the base 106 in both the axial and radial directions with respect to the disks 108 so as to protrude onto the disks 108 the correct distance. These precision manufacturing constraints increase the complexity and cost of the disk drive.
There is, therefore, a need to improve shrouding within a disk drive without incurring the complexity and expense of precisely machining and precisely installing additional components.